1. Field of the Invention
The present invention relates to the field of utilizing a robot to process and assemble small devices having small parts or components. More particularly the present invention relates to the field of utilizing a robot with a rotatable wrist to move a rotatable pallet which holds a plurality of small parts, delivering the rotatable pallet sequentially to a plurality of fixed work-stations, moving the pallet to move the part as necessary relative to the station for the station assembly and processing functions, and then rapidly indexing between parts in milliseconds by rotating the pallet. By tracking pallet and nest identity the pallet enables integration of an entire factory information system down to the individual assembly.
As one of the important applications, the present invention method and apparatus will be illustrated in the assembly and processing of intraocular lenses, which are lenses approximately 1/4 inch in diameter that are surgically implanted and are difficult to handle due to their small size. They are also particularly susceptible to contamination and damage during human handling.
2. Description of the Prior Art
Cylindrical coordinate and selective compliance articulated robot arm (SCARA) robots now perform many industrial assembly and processing tasks. Primary uses for robots in assembly and processing are those where a specialized operating head is carried by the robot and moved to a fixed part or array of parts, for operations such as painting, welding, and soldering. More commonly, the robot is used as a programmable long-reach pick and place wherein it picks up the component parts from an array of locations and places them in assemblies at other locations. In the electronics industry, robots are commonly used to move components from part feed tubes or vibratory feeders to locations on the surface of printed circuit boards which move on a linear conveyor through the work cell.
In many cases of assembly and processing by robots, the assemblies are delivered to and removed from the robot cell traveling on pallets through or adjacent to the robot. In contrast to the present invention, the robot does not pick up the pallet to perform the operations. Robot productivity is limited by the time-to-index the part pallet, usually two to four seconds, by the distance between the source of components and the point where they are used, usually four inches to several feet, and by the number of tasks that can be accomplished with the particular tool on the robot end effector in the cycle time available. It takes from two seconds to five seconds for a typical robot to perform a complete part pickup cycle, including picking up the part and moving it to the work assembly. Because of the robots' limited work capacity, they are often placed adjacent to pallet transfer lines wherein they accomplish only part of the complete task of assembly or processing along a production line.
These prior art operating modes mimic human motions used in performing similar tasks and have not utilized a significant capability of said robots when they are equipped with rotatable wrists to index between parts in milliseconds.
When a human needs to process parts that are located in various locations, such as at each corner of a room, he would typically use a collection of parts on a tray of a single or multiple rows of parts. He would move to the first station, process all those parts, then move to each successive station until the process or assembly was completed. This invention is a precision tray and precise method for using such tray for moving assemblies that is particularly effective for precision robots equipped with rotating wrists.
A very common way to efficiently assemble or process parts in the millions per year is to provide an indexing central dial with part nests arrayed around it and a series of simple fixed stations each performing a limited assembly, processing, or inspection function. Typical times-to-index parts between stations six inches apart are 1/3 to 1/2 seconds. Importantly, the nests are at rest in the processing station and the station equipment must supply all of the motions required for the process at that work-station. Such equipment for custom parts is very costly to design and is generally limited to a very specific sequence of operations. When the process changes, such dedicated equipment must frequently be scrapped and a new machine designed. Therefore, from small quantities up to relatively large lot quantities, humans are utilized. However, when the parts are very small, are damaged by human handling, or are damaged by the debris shed by humans, efficient robotic assembly is economical at much lower lot sizes.
Some progress has been made in utilizing robots in small parts assembly, as shown in U.S. Pat. No. 4,543,702 issued to Wada, which discloses a method and apparatus for automatic assembly of lipstick. Wada employs two robots working in conjunction, each operating within the full range of its operating envelope. The first robot is equipped with fingers for clamping molds, and the second is equipped with finger-plates for clamping bottles and holding nozzles. Both robots are movable in three dimensions. Work-stations located around the work profile of the first robot include a mold supply unit, a material charge unit, a cooling unit, and a defective mold unit. The indicated operations are performed at each respective station. The product of the initial operations is then placed on a station from which the second robot can reach it. Work-stations around the work profile of the second robot include a bottle supply unit, a bottle draw-out unit, a stick draw-in unit, and a capping unit, all within the operating envelope of the finger plates and suction holders of the second robot. All these units operating in conjunction provide a fully automatic apparatus for assembling lipsticks and similar cosmetics. Such tooling is intended to always remain in the robot station and it is not assembling and processing small parts in a generic way.
For processing and assembly of small parts, some robots are equipped with multiple tools, either by having an array of tools mounted on the wrist head, or by a tool exchange device. The operating wrist head on the robot can be altered during processing by using a tool exchange device such as the one shown in U.S. Pat. No. 4,359,815 issued to Toyoda which discloses a machining center equipped with a robot arm to change cutting tools in a machining center, and to place a work-piece on this work table and remove it therefrom.
U.S. Pat. No. 4,664,588 issued to Newell discloses a typical mechanism required for a robot to change work tools. The assumption is that for each different task to be accomplished, the robot must be provided with such mechanisms, very expensive specialized robotic tools, space within the cell for storage of all the non-active tools, and must sacrifice time in making the exchange. The present invention changes work-stations instead of tools. However, for some robots, both the present invention and all prior art devices such as specialized tools and tool exchange mechanisms can still be utilized in the same robot work cell and as an integral part of the processing cycle.
Progress is also being made in assisting the robot to carry more than one part in its pick and place function by adding an array of part grippers. At least one manufacturer offers a robot wrist head that uses a circular array of part grippers rotating vertically about a horizontal axis to either present different part grippers or to pick up multiple parts for pick and place operations. Each of the grippers is positively controlled and the operation with the part is performed directly under the wrist head of the robot.
In 1984, Seiko Instruments, a robot manufacturer, disclosed a robot with an end effector having a circular array of four part grippers rotating in the horizontal plane under the robot wrist head. The device permits picking up to four parts from one point for placement in some other location. Because each gripper is expensive and must be individually controlled by the robot, the gripper array normally remains on the robot wrist head during operations and the gripper array has had very limited utility.
Since the mid-1980's robots have not fundamentally progressed in the ways they are used to assemble small parts. However, payloads on some robots suitable for the present invention have increased from 5 pounds to 55 pounds while robot prices have remained essentially the same, declining significantly in real dollar terms. Thus, small parts suitable for the present invention may be assemblies weighing up to perhaps 5 pounds each for which prior art normally installs expensive conveyor systems and multiple robotic cells each doing a small portion of the work.
The above-described prior art does not disclose an apparatus that would permit the convenient and easy assembly of a wide variety of articles having small parts, where tooling for a multitude of processing functions is economical; and that is flexible enough to permit quick and relatively easy changes to assemble completely different articles.
Therefore, there is a need for an automatic robot apparatus that can provide for fully automatic processing and assembly of articles having a number of small parts by much better utilizing the unique capabilities of said robots, increases the number of parts that can be processed or assembled in a given time, and is readily adaptable for production of significantly different articles having short production runs.